During various surgical procedures, it is often necessary or desirable to occlude a blood vessel. Once such procedure is cardiopulmonary bypass (CPB) which is commonly used during a variety of cardiac surgical procedures. The essential goals of CPB for heart surgery are to provide life-support functions, a motionless, decompressed heart, and a dry, bloodless field of view for the surgeon. In a basic CPB system, oxygen-poor blood is drained by means of gravity or is siphoned from the patient's venous circulation and is transported to a pump-oxygenator, commonly know as a heart-lung machine, where the blood is exposed to a gaseous mixture that eliminates carbon dioxide and adds oxygen to the blood. The oxygenated blood is then returned or perfused into the patient's arterial circulation for distribution throughout the entire body. This process requires a venous drainage cannula (or cannulae) to be placed into the right side of the heart (typically the right atrium), or directly into the major veins, (e.g. the superior vena cava (SVC) and/or inferior vena cava (IVC), or through peripheral vein access sites (e.g. the femoral vein), to drain unoxygenated blood from the patient and deliver it to the heart-lung machine. Similarly, an arterial or aortic perfusion cannula is placed in the aorta or another large peripheral artery (e.g. the subclavian or common femoral artery), to return or perfuse oxygenated blood to the patient. The heart and lungs of the patient may thereby be effectively bypassed, thus allowing the surgeon to operate on a bloodless heart.
The insertion of the arterial (aortic) perfusion cannula is usually performed in the following fashion. After the patient's chest has been opened and the pericardium (the protective sac around the heart) has been entered, two concentric purse-string sutures are placed in the anterior wall of the ascending aorta just upstream of the brachiocephalic trunk. A "choker" tube or sleeve is positioned over the trailing ends of the suture threads to act as a tourniquet for tightening each of the purse-string sutures. A small incision centered within the purse-string sutures is then made through the wall of the aorta into its lumen. The aortic perfusion cannula is quickly inserted through that incision into the aorta, taking care to minimize the escape of blood from the puncture site. The purse-string sutures are then tightened by means of their respective tourniquets to seal the aortic wall around the perfusion cannula in order to prevent the escape of blood from the aorta. Air is evacuated from the perfusion cannula as it is joined by a connector to tubing from the pump-oxygenator. A cross-clamp is placed on the aorta just downstream of the aortic root and upstream of the perfusion cannula to ensure that no blood flows back into the aorta during CPB.
The venous drainage cannula(e) may be inserted in a similar manner directly through an incision in the right atrium of the heart or into the superior and/or inferior vena cava for connection to the drainage side of the pump-oxygenator.
Once the requisite cannulae are in place and the connections are made to the heart-lung machine, CPB is instituted by allowing unoxygenated blood returning to the right side of the heart to be diverted through the venous drainage cannula(e) into the pump-oxygenator where it is oxygenated and temperature-adjusted. From there, the blood is pumped into the patient's arterial system via the arterial or aortic perfusion cannula to provide oxygen-rich blood to the patient's body and brain.
After CPB has been established, a process known as cardioplegia, which literally means "heart stop," is typically used to arrest the beating of the heart, and in some procedures, to provide oxygen to the myocardium. Cardioplegia is administered by delivering a cardioplegic solution, such as potassium, magnesium or procaine, or a hypocalcemic solution, to the myocardium by one or a combination of two generally known techniques, antegrade and retrograde perfusion.
The antegrade administration of cardioplegia involves the infusion of fluid through the coronary arteries in the normal direction of blood flow. This antegrade flow may be accomplished with a single cardioplegia catheter or a cannula having a distally extending needle obturator. The needle is inserted into the aorta upstream of the aortic clamp and cardioplegic solution is injected into the aortic root and drains in the normal direction of blood flow into the coronary ostia, through the coronary arteries, and into capillaries within the myocardium.
Cardioplegic arrest and CPB are commonly employed during cardiac surgery for treating coronary artery disease and heart valve disease, among other cardiac diseases including atrial and ventricular septal defects. In coronary artery disease, a buildup of stenotic plaque in the coronary arteries causes the arterial lumen to narrow or become completely occluded, restricting or cutting off the blood flow to the heart muscle, which may ultimately result in a myocardial infarction, commonly known as a heart attack. Heart valve disease includes two major categories, namely valvular stenosis, which is an obstruction to forward blood flow through the heart valve, and regurgitation, which is the retrograde leakage of blood through the heart valve. Most commonly, valvular stenosis occurs in the aortic valve while regurgitation is typically a congenital condition affecting the mitral valve.
The major surgical intervention of coronary artery disease is coronary artery bypass grafting (CABG). In this procedure, while the patient is under general anesthesia, a median sternotomy or major thoracotomy is made, the patient is placed on full CPB, and the heart is placed under cardioplegic arrest. Similarly, when it is necessary to repair or replace a malfunctioning heart valve within a patient, the procedure is accomplished through a median sternotomy (typically for an aortic valve procedure) or major thoracotomy (typically for a mitral valve procedure), requiring general anesthesia and total CPB with cardioplegic arrest.
While conventional CABG and valve procedures generally have high efficacy, they are highly traumatic and have significant complications associated with median sternotomy or major thoracotomy, resulting in a prolonged, painful, and expensive recovery. Such conventional procedures also tend to be complicated by the presence of a large number of instruments, sutures, clamps and cannulae, in addition to the relatively large size of the cannulae for CPB and cardioplegic arrest, which potentially inhibit access to the heart, making access via an invasive incision (sternotomy or thoracotomy) unavoidable.
Less invasive surgical techniques and instrumentation have evolved for performing CABG which eliminate the need for a median sternotomy or major thoracotomy, as well as the need to stop the heart and place the patient on CPB. A small incision, such as a mini-thoracotomy or mini-stemotomy, is made in the patient's thoracic cavity and spread open. Specialized retractors are used for accessing arterial conduits, such as the internal mammary arteries, and specialized instruments are used to stabilize the motion of the beating heart while the anastomosis is being established. Although these less invasive surgical procedures have been highly successful, having patency rates as high as conventional CABG procedures and greatly reducing the physical trauma to the patient, a less skilled surgeon doing a highly complex case may still need to place the patient on CPB and stop the heart. As for valve repair and replacement procedures, a less-invasive, beating-heart approach has yet to be perfected.
Also, endoscopic methods and instruments have been developed for performing CABG as well as for performing heart valve repair and replacement. In such procedures, an endoscope and the surgical instruments are introduced and manipulated within the patient's body through small percutaneous incisions or puncture sites. The entire surgical procedure can then be viewed by the surgeon through the endoscope. With such procedures, the cannulae and catheters for establishing CPB and cardioplegic arrest are also introduced percutaneously or via a cut-down in a peripheral vessel and then endovascularly advanced into the patient's vasculature to the desired site.
Most commonly in such endovascular procedures, arterial perfusion of blood is accomplished via cannulation of the femoral artery with the retrograde delivery of an aortic occlusion balloon to the ascending aorta. However, this method of perfusion is associated with a high incidence of complications, such as dissection of the aorta and migration of the occlusion balloon. More particularly, when the balloon is inflated to occlude the aorta, the wall of the aorta is often deformed radially outward to ensure a substantial seal. Such deformation of the wall of the aorta, especially during inflation, may dislodge embolic material such as plaque from the wall of the aorta, which may then flow downstream, for example to the brain, thereby harming the patient. Further, because the wall of the aorta may be distorted substantially when the balloon is inflated, particularly if the balloon is excessively inflated, the wall of the aorta may be damaged or may even rupture.
Occlusion balloons may also "walk" or drift within the aorta because of the substantial pressure of the blood being delivered through the arterial cannula and/or the pumping of the heart prior to cardioplegic arrest. If the inflated balloon travels downstream, it may at least partially occlude the brachiocephalic trunk, thereby reducing and/or preventing blood delivery to the brain or elsewhere, which may again cause great harm to the patient.
Alternatively, oxygenated blood may be returned to the patient's arterial system by use of "central" cannulation, wherein a perfusion cannula is placed directly into the ascending aorta through a puncture in the aortic wall.
As discussed previously, when central cannulation is used during a cardiac surgical procedure, a cross clamp is typically used to occlude the aorta. Such clamps typically include a pair of jaws that engage an outer surface of the aorta and compress opposing sides of the vessel wall together until the vessel's lumen is squeezed shut. Oxygenated blood is delivered into the ascending aorta distal or downstream of the clamp, for example using an arterial cannula as discussed above. With the clamp in place, oxygenated blood perfuses the patient's body in a substantially normal direction, and is prevented from traveling proximally or upstream into the heart. In addition, cardioplegic solution may be delivered proximal or upstream of the clamp into the aortic root. The cardioplegic solution is thereby directed into the coronary ostia in an antegrade manner, and not into the patient's arterial system.
Conventional clamps, however, have many risks associated with their use. For example, as mentioned above, patients undergoing cardiac surgery often have a substantial build-up of plaque on the interior wall of the aorta which may be brittle. The engagement and release of the clamp may break-off and dislodge pieces of the plaque from the wall of the aorta, creating emboli which in turn can cause severe harm to the patient, such as a stroke.
In addition, the pressure applied by a clamp and the resulting deformation of the aorta may damage the wall of the aorta itself. Further, a clamp applied to the outer wall of the aorta may damage connective tissues or nerves, for example those extending between the aorta and the pulmonary arteries.
Therefore, there is a need for an improved system for occluding a blood vessel during surgery, for example the aorta during cardiac surgery, that minimizes the risk of harm to the patient and/or that facilitates minimally invasive surgical procedures.
The present invention fulfills these needs, and provides further related advantages, as will become apparent from the following description and accompanying drawings of the invention, taken in conjunction with the appended claims.